As bandwidth demand for indoor wireless users continues to grow, cellular operators are trying to explore bandwidth provisioned from indoor, in addition to providing bandwidth from outdoor. Because of the physical nature of radio signals, however, cellular operators have faced difficulties to provide full coverage for indoor users. Femtocell is developed to enhance indoor coverage by reusing the licensed spectrum as part of the cellular network infrastructure. Femtocell is anticipated to be an important feature to support extreme high-speed transmission for 4G systems. Both IEEE 802.16m and 3GPP are currently developing femtocell technology as part of the standards for WiMAX 2.0 and LTE-Advanced systems. As more small-coverage femto base stations are deployed into existing wireless networks, it becomes more popular for wireless networks to have overlay macro-femto network architecture.
FIG. 1 (Prior Art) illustrates an overlay macro-femto network architecture and radio resource allocation in wireless OFDMA network 10. Wireless OFDMA network 10 comprises a macro base station MBS11 serving cell 17, two femto base stations FBS12 and FBS13 serving cells 18 and 19, and a mobile station MS14. The cell coverage of FBS12 and FBS13 is much smaller than the cell coverage of MBS11. In addition, the cell coverage of FBS12 and FBS13 overlaps with the cell coverage of MBS11. As illustrated in FIG. 1, mobile station MS14 is located in the service coverage of cell 17 and receives desired radio signals 15 from its serving base station MBS11. Because of the overlay macro-femto network architecture, however, MS14 is also located close to cells 18 and 19, and receives interfering radio signals 16 from FBS12 and FBS13.
There are different alternatives in allocating radio resource in wireless OFDMA networks. Two different resource allocation schemes are illustrated in FIG. 1. In the first example, frequency reuse three (i.e., FR=3) is used so that each base station uses a different frequency spectrum for data transmission. In the second example, frequency reuse one (i.e., FR=1) is used so that each base station uses the entire frequency spectrum for data transmission. While frequency reuse three provides high SINR to meet the minimum quality of service (QoS) requirement, it suffers from low cell throughput and resource utilization. On the other hand, while frequency reuse one achieves higher cell throughput and resource utilization, it suffers from low SINR and poor QoS. Therefore, in macro-femto overlay wireless networks, it is desirable to have flexible radio resource management schemes to improve the spectral utilization efficiency as well as to meet minimum QoS requirement.